Method of and apparatus for screening paper pulp



E. J. TRIMBEY May 3, 1932.

METHOD OF AND APPARATUS FOR SCREENING PAPER PULP 5 Sheets-Sheet Filed Sept. 6, 1928 MATTORNEY E. J. TRIMBEY um'rnon 01-" AND APPARATUS ron scnssume PAPER rum :5 Sheets-Sheet 2 Filed Sept. 6, 1928 A ATTORNEYS y 1932- E. J. TRIMBEY 1,856,176

METHOD OF AND APPARATUS FOR SCREENING PAPER PULP Filed Sept. 6, 1928 3 Sheets-Sheet A; ATTORNEY 5 Patented May 3, 1932 EDWARD J. TRIMBEY, 0F GLENS FALLS, NEW YORK METHOD OF AND APPARATUS FOR SCREENING PAPER PULP Application filed September 6, 1928. Serial No. 304,207.

This invention relates to the screening of paper pulp, or similar substances, and has for its object the provision of an improved process and apparatus therefor so as to leave 85 fewer coarse pieces or slivers in the screened pulp, and less good fibre in the rejections or screenings, to perform this separation with the consumption of a minimum expenditure of power, to perform this separation at an 10 increased rate, and at the same time to prevent the admixture of air with'the pulp during the process of screening and to also prevent undue agitation during the process and thus reduce or eliminate foaming.

It is a well-known fact that logs in a stream tend to aline themselves with their axes parallel to the direction of flow, and the same holds true of pulp fibres which by their relative proportions of diameter compared to,

their length are comparable to logs. If the coarse fibres approach the screen plate end on as many do when the pulp is forcibly sprayed or thrown against stationary screen plates, as in many of the screens now in use in the pulp and paper mills, or, if the fibres are drawn or sucked through the perforations by the pumping action set up by rapidly revolving cylindrical screen plates, as in another type of screen in general use, many of them pass through the perforations into the screened pulp space and the result is a prod not which is inferior due to the presence of an appreciable amount of coarse and undesirable fibres.

According to the present invention I cause the fibres to line up parallel to the surface of the screen plate before they reach it and then move them through the perforations lateral- 1y. Thus, the coarse fibres, the length of which is greater than the diameter of the perforations, cannot pass through, whereas had they approached the openings end on many would have passed through even though their lengths were several times the diameter of the perforations, provided only that their diameters did not exceed this diameter.

In order to accomplish this result, I bring the unscreened pulp to a high rotative velocity in a stationary cylindrical screen by means of a rotor before it comes into contact with the stationary screen plates. By gradually building up a high rotative veloc ty in the dilute liquid pulp mass before the fibres come into contact with the screening surface, the desirable fibres and especially the slivers or fibres which are too long and coarse for use in first quality pulp, tend to-straighten out with their axes parallel to the direction of flow which is a circular path determined by the cylindrical body of the-screen. Being at a high rotative speed the centrifugal force thus developed causes the liquid and the desirable pulp fibres to pass through the perforations or slots while the coarser particles continue to revolve at this same velocity, being carried around by the rotorand moved to the rejection outlet by means of inclined elements on the periphery of the rotor.

In many designs of screens While the entering pulp may have considerable longitudinal velocity no advantage is taken of this potential energy to assist in the screening operation, and the liquid pulp while relatively at rest as regards rotative velocity is violently caught up by vanes or impellers and hurled against the screen plates with undesirable agitation and with considerable loss and waste of power. According to the present invention the entering pulp, which on account of the pressure or headon the supply is travelling with a rectilinear velocity of several hundred feet per minute, is turned through an angle of nearly ninety degrees and issues centrally of the screen chamber into the rapidly revolving rotor with this same high velocity undiminished but transformed into rotary mot-ion and ready to be picked up by the vanes of the rotor. Thus; all of the energy due to the initial longitudinal velocity of the entering pulp is conserved. The screen chamber and rotor are constructed so that the linear velocity of the pulp is greatly increased by the time the pulp particles reach the screen with little if any change in angular velocity, and this without any abrupt change and consequent loss in energy. There is therefore an entire absence of agitation, the pulp mass passing along smooth stream lines to the periphery of the screen chamber where the good fibres pass through. W

I u I c is kept in rotation Byoperating with the central portion of the screen chamber full of pulp, with a closed connection to the supply, and with almost entire freedom from agitation the tendencyto produce foaming when handling certain kinds of pulp or pulp mixtures is reduced to a minlmum.

As the water and the finer fibres pass through the screen plate, the residue consisting the rejections and some good fibres becomes too concentrated for the good fibres to readily find their way through the mass and to the openings in the screenplate, and if some, means were not provided for diluting the pulp. at this point a varying amount of good pulp would jections. Due to the high rotative velocity the mass of liquid pulp tends to form a layer or wall along the inside of the cylindrical screen plate surface, and this wall of pulp by the rotor. In order to wash the adhering good fibres from the coarse rejected fibres and also to assist in freeing the screen itself, I add water, preferably white by a force moving water, on the inside of the rotating pulp wall. This water may be introduced in t e direction of flow of the pulp and with ap reciable velocity. through The water thus adde is carried the rejected fibres by centrifugal action, washers off the adhering good fibres,v

and frees the coarser fibres for ejection from the screen.

When .the rotatingpulp approaches a slot or hole in the screen plates it is acted upon parallel to the surface of 1 the plate or tangential to the curved surface.

" into the path of I of pulp and As it comes to the nearer edge of the hole or slot it tends to pass through the hole but it is also acted upon by the centrifugal orce' which is acting normal to the surface of the plate. The line of action is therefore along the resultant of the two forces. Moving thus at an angle there is only a very small proportion of the area of the ordinary normally drilled hole which is subject to the direct pressure of this resultant force. ticles of pulp and water, tending also to move at an angle to the surface of the plate, the vertical walls of the hole and are diverted the particles which would otherwisehave a small area. In this way only a portion of the hole isefiective as regards the passage water. According to the present invention the holes or slots may be made with their axes at an angle to the surface of the plate preferably at an angle of approximately 45. Approximately the entire area of the hole is then efiective for passing pulp and water, which greatly increases the capacity of the machine.

In the accompanying drawings I have illustrated a preferred embodiment of the apparatus of my invention and in which my imbe carried out with the re- I Other parstrike direct passage through theproved method can be carriedout; In these The screen illustrated comprises a base casting 1, and a top casting 2 which is supported by the upright pieces 3 and 4, one of which, 4, serves as the outletfor the screened pulp. These upright pieces, 3 and 4, serve to form part of the outer cylindrical body or casing of the screen, the curved pieces 5, which are bolted to 3 and 4, making up the remainder. To give a water tight connection between the side pieces 5 and the pieces '1, 2. 3 and 4, rings 6 are cast integral with 1 and 2 and in these rings grooves 7 are cut to receive packing strips. Longitudinal grooves are also provided at 7 when pieces 5 are bolted in place they draw against a continuous strip of fibrous packing. Concentric with the cast rings 6 which form the backing or support for side pieces 5, are other rings 8 to serve as supports for. the screen plate 9 which is in two semi-cylindrical pieces attached to frame 10, also in two sem1-cylindrical pieces. The screen plates which are perforatedeither with round holes or with narrow slots, depending upon the nature of the pulp to be handled, are bolted or riveted to the frames 10, which are bolted together along longitudinal joints at.11 and thus clamp securely aroundthe rings.8.

Base casting 1 carfiies a vertical shaft 12 mounted in a ball-thrust bearing 13 at the bottom and guidedand supported at the upper 15 isretained in place by gland 16 andis used to prevent dirt or water from entering thebearing and also to retain the lubricating grease which from time to time is forced in through the connection 17. Packing 18 is placed around shaft 12 above ball bearing 14 to prevent Water and pulp from working down into the bearing and is. retained in place by follower gland 19. It also serves to prevent lubricating grease, introduced through connection 20. from contaminating the pul Shaft 12 carries a bevel gear 21 driven lly steel pinion 22 on shaft 23, and is driven by pulley 24, or by sprocket and chain when motor drive is used. Shaft 23 is carried in the ball bearings 25. On the upper end of shaft 12 is a bronze in 3 and 4 so that end by the ball bearing 14. The packing outlet 33 they are conducted away casting 26 having four blades or vanes 27 which unite the hub 28 and the bell-shaped body 26,- and extend outward from the bottom so as nearly to reach the cylindrical screen plate 9. That portion of each vane which is within the body 26 is in a vertical plane which would pass through the axis of the shaft, while the ends which extend outward from the body are curved backward in the direction of rotation but the vertical elements are still parallel to the axis of the shaft. These vanes are in two pairs, the ends of one pair being segments of a, cylinder as shown at 29, while the ends of the other pair are curved backward in the direction of rotation for a short distance as shown at 30 and then continue as fiat surfaces to which are attached the lower ends of elevators 31 At the top of the rotor body 26 are two radially extending arms 32 which serve as supports for the upper ends of the elevators" 31. These arms 32 are not vertically above the Hat ends of the vanes at 30, but are placed several degrees backward as compared with the direction of rotation; this is to give a warp to the elevators 31 so that they will tend to lift or elevate the slivers or rejections and so bring them'to the rejection outlet 33. It will be noted that the diameter of the enclosed portion of the rotor at the receiving end is less than half that of the cylinder formed by the screen plates, and that due to the bcll-shaped form of the rotor and the convex center of the base of the screen chamber the area of the passages and the diameter of the rotor are gradually increased until,

: after emerging from beneath the body 21;, theblades 27 extend out nearly to the screen plate 9. In this way, without the loss of energy which would be caused by abrupt changes in velocity. and with but little if any change in anghlar velocity from that which it had when emerging from the inlet 41, the linear rotative velocity is greatly increased and reaches the desired value by the time the pulp particles reach the screen plate, and there is an entire absence of agitation.

Rejection outlet 33 is cast with, or attached to, the under side of top piece 2 and comes flush with the screen plate 9. reaching down into the space just inside of the screen plate. Elevators 31 are of such a length that they will just pass beneath the bottom of outlet 33 and their edges are almost parallel to and at a short distance from the screen plates. The purpose of these elevators is to keep the mass or wall of rotating pulp moving with the same rotative velocity which it had at the bottom of the screen body and also to lift or elevate the rejections to the outlet 33. After the rejections have been thrown into by pipe 35, water added at connection 34 assisting in conveying them into the outlet pipe.

For freeing the good fibres from the rejections before they reach the outlet 33, White water is admitted from pipe 36 into the curved spout chamber 37 which projects from the under side of the top casting 2; the object of the curved shape which is concentric-with the adj acent screen plate 9, is so to direct the water as it leaves will be movingin the samedirection as the revolving wall or. body of pulp within the screen, the velocity with which it issues from spout 37 being determined by the pressure of the entering water.

T 0 remove pieces of iron, heavy grit or other foreign substances which might injure the screen plate, a receptacle or chamber 38 is provided in the base 1, at the bottom of the sloping section such foreign materials will drop into the space thus providedand'can be removed from time to time through the hand plate 39.

The supply enters from the inlet chamber 41 and inlet pipe 40, or enters chamber 41 from a supply box or head box. Inlet chamber 41 is provided with three or more curved vanes 42 similar to the runner of a waterwheel. This chamber 41, which is stationary and is bolted to the top casting 2, projects downward some distance into the rotor, coming nearly .to the upper edge of the blades 27, and into the mass of pulp within the screen chamber. The vanes 42 which are cast integral with the chamber 41 are so arranged that at the inlet end their planes are vertical and pass through the axis of the chamber, but as they proceed downward they are warped, slightly at first and then more abruptly, until at the bottom or lower end of 41 they are practically horizontal. The object of this change in the-plane of the vanes is gently, and without disturbance or agitation, to change the direction of the stream lines of the entering pulp from a rectilinear direction parallel to the axis of the chamber and'of the screen, path about the axis of the chamber.

In Figure 5 I have illustrated a section of my improved screen plate showing the angular position of the screen perforations. The rotative force imparted to the pulp by the rotor vanes and the elevator plates tends to cause the fibres to move along a line tangential to the sc 'een chamber. The direc tion and magnitude of this force is indicated in the drawings by the dotted line T. At the same time each fibre is acted upon by centrifugal force which acts radially and is indicated by the dotted line C. Thus, the fibres when passing through the screen perforations tend to move along the resultant of these forces, the dotted line H in the figure. In order to attain the maximum etliciency from the screen plates I have therefore, in accordance with the present invention, cut the per forations with their axes along the line R,

the chamber or spout 37 that it to a circular which makes an angle of 45 withboth the tangent and the radius. I shall now review the operation of the apparatus which has just been described and point out the manner in which my improved method is employed. The unscreened pulp passes from the inlet pipe 40 into the inlet chamber 41 where curved blades 42 convert the rectilinear motion of the incoming pulp into rotary motion. The pulp is thus caused to enter the screen chamber rotating at a relatively high rate of speed but without additional energy input. ,Here it immediately encounters the pulp already in the screen chamber which is also being rotated by the rotor blades 27. The angular velocity of the pulp at the center of thescreen chamber is not substantially greater than that of the incoming pulp so thatthere is no cause for agitation, and the incoming pulp flowssmoothly into the already rotating mass.

This absence of agitation, freedom from violent and abrupt changing of velocities and of stream-line forms, together with the utilization of a very large part of the potential energy in the entering pulp, reduce to a minimum the outside power required. As the rotation continues, the pulp passes down the sloping bottom of thechamber and under the flaring bell-mouth of the rotor. As it passes outward toward the screen plates the angular velocity remains substantially constant, but the linear velocity is correspondingly increased so that by the time the pulp reaches thescreen plates it has attained a relatively high linear speed and forms a liquid wall along the inside of the screen plates in accordance with the well-known laws of hydraulics. This rapid linear flow of the pulp has caused the fibres to aline themselves parallel to the direction of flow which is, of course, parallel to the screen plates and the fibres therefore approach the screen plates transversely. Thus, the coarser fibres being longer than the diameter of the screen perforations pass by while the finer fibres are. moved through the'perforations under the action of the centrifugal force acting upon the whirling mass. As the fibres are also impelled by the rotative force imparted bythe rotor and tend to move tangential to the screen chamber, their trajectory when passing through the screen perforations is resultant of the two forces and for this reason the screen perforations are cut at an angle of 45. 1

The screened pulp which enters the annular space between the outer shell or casing 5 and the screen plates is eventually removed through the outlet 4 but the level of this screen pulp is maintained at least as high as the level of the unscreened pulp wall within the screen chamber for purposes which I shall now describe, Althoughthe rotation of theentire mass of unscreened pulp tends to pu p free, nevertheless, a ifibre does gathir s the elevator plates 31, carried by the rotor, pass over the inner face of the screen plates they perform not only the two functions, already noted, namely maintaining the pulp mass in rotation and guiding the rejected fibres to the outlet 33, but they also assist in freeing the screen plates of-course fibres. As they pass through the pulp a momentary diminution of pressure occurs in their wake. This diminution, brief though it be, is sufficient to permit water from the screened pulp in the outer annular space to back through screen perforations and loosen the fibres whichmay face, which fibres are then moved upward along the screen face by the elevator plates 31 and ejected through the outlet 33.

j Many of these rejected fibres, however, are

associated with fine fibres which would be lost unless steps were taken to remove them before the coarse fibres are ejected. For this purpose, and for the additional purpose of further screen plates, thinning water, preferably white water, is introduced into the screen chamber through the water pipe 36 and curved chamber 37'. This water is moving in the same direction as the mass of the pulp, being so directed by the sh ape andlocation of the spout 37, and as this water distributes itself over the inside surface of the pulp layer it is caught up by the revolving pulp layer and by the arms 32 and elevators 31 and almost instantly attains the same velocity as the mass. As soon as this takes place cenning water 1s forcibly carried through the mass of rejections and good fibres carrying the good fibres with it to and through the perforations in the screen plate, while the coarser-particles now washed free of good fibres are carried upward by the combined action of centrifugal force and the warped shape of elevators 31 and ejected from the outlet 33 and pipe 35, being carried along by the water admitted at 34.

By the practice of the present invention a very tho rpugh screening isflefiected, very few coarse fibres passing through the screen plates with the fine fibres, and very few fine fibres being carried to waste-with the coarse fibres. The power consumption is low due to the utilization of the energy of the incoming and the elimination of violent changes have collected on the inner loosening the fibres adjacent the in directional flow and velocity. A high capacity per square foot of floor space occupied and per square foot of screening surface employed is also obtained. By keeping the inlet portion of, the body of the screen full of.

stock rotating at high velocity centrifugal force causes a layer or wall of stock to extend along the screen plates so that practically the entire screening area is in use at every instant, and due to the pressure set up by the centrifugal force, large quantities of good pulp are passed through the screen plates. The rapid rotation of the entire mass of pulp along the inside of the screen plate tends to keep the perforations free from clogging. This freedom from clogging and the continuous service of practically every square inch of the perforated or slotted surface of the screen plates together with the pressure with which passage of pulp through the perforations or slots is accomplished give greatly increased capacity as compared with other screens where many of the perforations are partially clogged with rejections and where only a portion of the screen plate is in service at any given instant. The angular location of the screen perforations also facilitates the passage of fine fibres without permitting the coarser to pass and thus makes for greater screening efficiency. Agitation and foaming are reduced to a minimum. This feature together with the low power consumption and high capacity make this type of screen especially suited for use in screening the mixture of pulp and other ingredients as it comes to the paper machines. When used in this connection the plates may be slotted if desired in place of being provided with round perforations.

I claim:

1. A pulp screen comprising the combination of a cylindrical screen chamber, an inlet for the pulp and means in the inlet for trans forming the rectilinear motion of the incoming pulp into rotary motion.

2. A pulp screen comprising the combination of a cylindrical screen chamber, a rotor for rotating the pulp within the chamber, an inlet for the pulp coaxial with the rotor and curved vanes within theinlet for converting the rectilinear motion of the incoming pulp into rotary motion.

A pulp screen comprising the combination of a. cylindrical screen chamber defined by cylindrical screen plates, a rotor within the chamber, a pulp inlet coaxial with the rotor, an outlet for rejected fibres at the top of the screen chamber, elevator plates carried by the rotor adjacent the screen plates and extending at a slight angle away from the direction of rotation along substantially the depth of the plates from the bottom of the chamber to the level of the outletand means for introducing thinning water at a point within and near the top of the chamber and in the direction of rotation of the rotor.

4. A pulp screen comprising the combination of a cylindrical screen chamber, the bottom of said chamber having a convex center, a bell-shaped rotor within the chamber, the flaring mouth of the bell receiving the convex center of the chamber bottom, a hub on the rotor, radial vanes connecting the hub with tion of a cylindrical screen chamber defined by cylindrical screen plates, and means for rotating the pulp within the chamber, the

perforations in the screen being cut ,at an.

angle and extending in the direction of retation of the pulp.

6. A pulp screen comprising the combination of a cylindrical screen chamber defined by cylindrical screen plates and means for rotating the pulp within the chamber, the perforations in the screen being cut at such an angle that the axes of the perforations shall lie along the resultant of the two forces acting upon the pulp, the one tangential to the path of rotation and the other, the centrifugal force, normal to the surface of the screen plate.

7. A pulp screen comprising the combina tion of a cylindrical screen chamber defined by stationary cylindrical screen plates, and means for rotating the pulp within the chamher, the perforations in the screen being cut at an angle of 45 and extending in the direction of rotation of the pulp.

8. A pulp screen comprising the combination of a cylindrical vertically extending screen chamber defined by cylindrical screen plates, a pulp inlet coaxial with the rotor, an

outlet for rejected fibres at the top of the screen chamber, elevator plates carried by the rotor adjacent the screen plates and ex tending at a slight angle. away from the direction of rotation along substantially the length of the plates.

9. A pulp screen comprising the combination of a cylindrical screen chamber defined by cylindrical screen plates, a rotor within the chamber, a pulp inlet coaxial with the rotor, an outlet for rejected fibres at one end of the screen chamber, elevator plates carried by the rotor adjacent the screen plates and extending at a slight angle away from the direction of rotation along substantially the length of the plates and means for introducing thinning water at a point within and near the outlet end of the chamber.

10. The method of screening paper pulp which comprises introducing the pulp at the center of a rotating mass of pulp at substantially the same speed and in substantially the same directions as the mass whereby agitation and foaming are avoided.

11. A pulp screen comprising the combination of a vertical cylindrical screen chamber, a rotor for rotating the pulp within the chamber, an inlet for the pulp coaxial with the rotor, and an imperforate annular member carried by the rotor and extending to a position adjacent but spaced from the bottom of the chainber said membenbeing coaxial with the rotor and adapted to preliminarily restrict dispersion of the incoming pulp and to conduct it to a position adjacent the bottom of the chamber.

12. A pulp screen comprising the combination of a vertical cylindrical screen chamber having a bottom provided with a tion, a rotor for rotating the pulp within the chamber, an inlet for the pulp coaxial with the rotor, and an annular; member carr1ed by the rotor and terminating in a flared end located over the convex. bottom of the chamber and ada ted to preliminarily restrict dispersion of the incoming pulp.

13. A pulp screen comprising the combination of a cylindrical screen chamber, a rotor tendin to a position adjacent but spaced from t e bottom of the chamber and adapted to preliminary restrict dispersion of the incoming pulp and conduct it to the bottom of the chamber, and blades carried by the rotor interiorly and exteriorly of the shell.

In testimony whereof I afiix my signature.

EDWARD J. TRIMBEY.

for rotating the pulp within the chamber, an

inlet for the-pul coaxial with the rotor,aan annular shell 0 greater diameter than the inlet carried by the rotor and arranged. to conduct the pulp entering through the inlet. to a position remote from the inlet, vanes carried y the rotor interio'rly of the shell, and means within the inlet for introducing the pulp in substantially the same direction as the direction of movement of the pulp within thechamber.

14. A pul screen comprising the combination of a cy indrical screen chamber, a rotor for rotating the pulp within the chamber, an inlet for the pulp extending into the chamber, an annular shell of larger diameter than the inlet and having a flared end for conducting the incoming pulp to a position remote from the inlet and vanes carried by the rotor and extending in a direction a-rallel to the axis of the rotor at a spaced istance from the exterior of the shell.

15. A pulp screen comprising the combinav tion of a vertical cylindrical screen chamber,

a rotor for rotating the pulp within the chamber, an inlet for the pulp disposed axially with respect to the chamber and vanes within the inlet for deflectin the incoming stream of pulp into the cham r in the direction of rotation of the rotor. 4

16. A pulp screen comprising the combination of a vertical cylindrical screen chamber,

a rotor for rotating the pulp within the chamber, an inlet for the pump coaxial with the rotor and an annular shell of appreciably less diameter than the screen chamber carried bythe rotor, said shell extending to a position adjacent butfspaced from the bottom of the chamber and adapted to preliminarily restrict dispersion of the incoming pulp and conduct it to the bottom of the chamber.-

17. A pulp screen comprising the combination of a verticalcyli'ndrical screen .chamber, a rotor for rotating the pulp within the chamber, an inlet for the pulp coaxial with the rotor, an imperforate annular shell pf a preciably less' diameter than the screen c amber-carriedby the rotor, said shell ex- 

